Binding
A property wrapper type that can read and write a value owned by a source of truth.
Declaration
@frozen @propertyWrapper @dynamicMemberLookup struct Binding<Value>Mentioned in
Overview
Use a binding to create a two-way connection between a property that stores data, and a view that displays and changes the data. A binding connects a property to a source of truth stored elsewhere, instead of storing data directly. For example, a button that toggles between play and pause can create a binding to a property of its parent view using the Binding property wrapper.
struct PlayButton: View {
@Binding var isPlaying: Bool
var body: some View {
Button(isPlaying ? "Pause" : "Play") {
isPlaying.toggle()
}
}
}The parent view declares a property to hold the playing state, using the State property wrapper to indicate that this property is the value’s source of truth.
struct PlayerView: View {
var episode: Episode
@State private var isPlaying: Bool = false
var body: some View {
VStack {
Text(episode.title)
.foregroundStyle(isPlaying ? .primary : .secondary)
PlayButton(isPlaying: $isPlaying) // Pass a binding.
}
}
}When PlayerView initializes PlayButton, it passes a binding of its state property into the button’s binding property. Applying the $ prefix to a property wrapped value returns its projectedValue, which for a state property wrapper returns a binding to the value.
Whenever the user taps the PlayButton, the PlayerView updates its isPlaying state.
A binding conforms to Sendable only if its wrapped value type also conforms to Sendable. It is always safe to pass a sendable binding between different concurrency domains. However, reading from or writing to a binding’s wrapped value from a different concurrency domain may or may not be safe, depending on how the binding was created. SwiftUI will issue a warning at runtime if it detects a binding being used in a way that may compromise data safety.